is this sleeping behavior normal?

My 4 hens start out the night all crowded into one corner of the coop. They have lots on room in there and by morning when I let them out they are on the ladder roost in there. But at night they jam in tight in the corner. Its weird looking.

Now, these 4 survived an ugly nighttime raccoon attack where 5 of their sisters did not. It must have been tramatic for them and I was wondering if this could bring on such nighttime behavior.

I haven't experienced it, but yes they can be traumatized by a predator attack. Some chickens may get over it quickly, but some may take quite a long time. They are very much individuals. Having said that, it's part of their survival instinct to mimic what the other members of their flock are doing. If one member of the flock is freaking, the others will usually decide it's with good reason and freak out too.

My broody chicken sleeps on top of her nonbroody chicken. It looks so weird, and I thought the sister on the bottom would protest, but she puts up with it. I guess this keeps the broody's chest nice and warm, as if she were sitting on eggs?

My Brahmas sleep in a multi-coloured pile in one corner of one pen. They have 2 pens to choose from (I have other chickens who go to bed later into the second pen), perches etc. but seem to prefer the floor.

They are led there by dominant rooster who is too heavy to get onto the perch.